Cordless telephone systems are known. Such systems typically transmit and receive over a frequency pair in full duplex mode over relatively short distances. Power outputs of cordless telephone systems are typically very low at less than 100 milliwatts. The relatively low power output may offer reliable service within a home and a yard proximate to the home.
The low power of the cordless telephone also provides another benefit in that a number of cordless telephones operating on the same frequency may operate in relatively close proximity. Where interference is experienced, provisions are typically provided within cordless telephones for a second operating frequency, selectable from within the telephone, to avoid interference.
Cordless telephones are typically constructed to interface with a public switched telephone network (PSTN) providing access to such PSTN system from a cordless telephone base site within the home. Other telephones are also typically connected to such system also within the same home. Such collection of telephones within the home comprises a party line on which a number of people may participate in the same conversation as a conference call.
Spread spectrum communication systems are also known. Spread spectrum systems are communication systems with a high inherent degree of resistance to interference from other transmitters. Spread spectrum systems achieve their resistance to interference by transmitting an information signal distributed over a relatively wide frequency bandwidth. Use of the wide bandwidth avoids a total blocking of signals from interference present on individual frequencies or limited bands of frequencies.
Two examples of spread spectrum communication systems are direct sequence spread spectrum (DSSS) and frequency hopping. DSSS systems achieve the wide band distribution of a message signal by encoding a signal with an output from a pseudo random number generator. Frequency hoppers, on the other hand, achieve a distribution of signals through an indexing format.
The indexing format used by frequency hoppers involves the transmission of a relatively narrow band information signal which is periodically indexed to a new frequency. Indexing of the transmission signal under frequency hopping format achieves noise immunity by a rapidly changing frequency format. Because of the rapidly changing frequency of transmission, noise present on one frequency tends to block only part of the information signal.
Because of the utility of cordless telephones and spread spectrum technology, a need exists for a way to implement spread spectrum technology to cordless telephones in a manner fully consistent with past services, including conference calling. Past telephone services within the home have offered conference call access to the PSTN through a number of hard-wired extension phones located throughout the home. A need exists for a way to offer such conference call features from remote handsets within a cordless telephone system without the need for hard-wired extension phones.